The present application is based on and claims priority from Japanese Patent Application 2000-112527 filed Apr. 13, 2000, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a plane commutator that has a disk-like commutator surface and a method of manufacturing such a commutator.
2. Description of the Related Art
A plane commutator that has a flat commutator surface is installed in a motor such as a motor of a motor-integrated fuel-pump unit. The plane commutator is comprised of a plurality of commutator segments made of a sintered carbon compound and insulated by slits from each other, a plurality of metal base plates, and a resinous boss member. The plurality of the commutator surface forms a flat commutator surface, and each of the commutator segments is connected to one of the metal base plates. Because the commutator segments are made of a sintered carbon compound, it is difficult to adopt heat treatment by fusing to a mass production line of the above plane commutators.
JP-A-9-46978 discloses a plane commutator which is comprised of a plurality of commutator segments, a metal base plate and a resinous boss member. The metal base plate has a contact portion in contact with the commutator segments at the surface opposite the commutator surface thereof, axial portions extending along the outer periphery of the boss member and terminal portions. The contact portion of the metal base plate has a plurality of openings in which resinous material is filled.
However, when an end of an armature winding of a motor is connected to the terminal portion by fusing, the axial portion thermally expands and gives stress on the peripheral portion of the resinous boss member, which may be damaged and broken.
For example, if the axial portion that is enclosed by a resinous material of the boss member expands in circumferential directions of the boss member, the resinous material may be cracked or damaged by the axial portion.
Therefore, a main object of the invention is to provide a plane commutator that may not be damaged even if the axial portion of the metal base member thermally expands.
In a plane commutator according to a main feature of the invention, includes a plurality of commutator segments made of carbon compound, a resinous boss member and a plurality of metal base plates, axial portions of the metal base plates are disposed on the outer periphery of the plane commutator in parallel with the outer peripheral portion of the boss member to separate the outer peripheral portion from the body portion of the boss member. Since the outer peripheral portion of the boss member is separated from the body portion of the boss member, the outer peripheral portion can move freely from the body portion and little stress is given even if the metal base plates thermally expand.
In a plane commutator according to another feature of the invention, the boss member includes a plurality of bridge portions extending in a direction substantially perpendicular to a direction of thermal expansion of the axial portion of the metal base plates to connect the outer peripheral portion and the body portion inside the axial portions of the metal base plates. Since the bridge portion is flexible, the outer peripheral member can move comparatively freely from the body portion, while the outer peripheral portion is more tightly anchored to the body portion.
According to another feature of the invention, a method of manufacturing a plane commutator including the following steps: soldering a disk member made of a sintered carbon compound to a cylindrical metal member to form a unit in which a base portion of the disk member is in contact with a contact portion of the cylindrical member; putting the unit into a mold die to mold the unit with resinous material to form a boss member; forming a bridge portion extending perpendicular to the axial portion of the cylindrical metal member to connect the body portion and the outer peripheral portion inside the axial portion; forming a plurality of radial slits in the disk member and the cylindrical member.